1. Field of the Invention
The present invention relates to a shock-absorbing packing material which is put in a gap between an electronic device such as a television receiver and a cardboard box when the electronic device is packed in the cardboard box.
2. Description of Related Art
A television receiver, which is also hereinafter referred to as “TV receiver” for short, is packed in a cardboard box at the time of factory shipment. In packing a TV receiver in a cardboard box, a shock-absorbing packing material is put in a gap between the cardboard box and the TV receiver. The shock-absorbing packing material is a foamed resin molding, and specifically a member which absorbs a physical shock to prevent the shock from reaching the TV receiver when the cardboard box with the TV receiver packed therein receives the shock owing to e.g. drop of the cardboard box or collision with other object.
FIG. 10 is a front-side sectional view showing the condition where a TV receiver is packed in a cardboard box, which is known in the art. FIG. 11 is a lateral sectional view of the cardboard box with the TV receiver packed therein as shown in FIG. 10. FIG. 12 is a perspective view of a shock-absorbing packing material conventionally used for a TV receiver. As shown in FIGS. 10 and 11, a TV receiver 3 is packed in a cardboard box 1, and each shock-absorbing packing material formed from a foamed resin molding is arranged in contact with adjacent four faces of the cardboard box 1. Now, in the description below, a corner portion formed by butting different exterior faces on each other is termed “an exterior ridgeline”, a corner portion formed by butting different interior faces on each other is termed “an interior ridgeline”, a point where different exterior ridgelines gather is termed “an exterior apex”, and a point where different interior ridgelines gather is termed “an interior apex”.
Shock-absorbing packing materials 92b arranged against a lower portion of the TV receiver 3 is disposed so as to support the lower portion of the TV receiver 3 from left and right sides thereof. Shock-absorbing packing materials 92a and 92c arranged against an upper portion of the TV receiver 3 are disposed so as to support the upper portion of the TV receiver from front and rear sides thereof.
The shock-absorbing packing material 92a shown in FIG. 12 is arranged so as to support the exterior ridgeline of the front side of the upper portion of the TV receiver. However, the shock-absorbing packing materials 92b and 92c arranged in the other places have a similar shape. As shown in FIG. 12, the shock-absorbing packing material 92a has: a first wall 921 which is an elongated member; a second wall 922 having the same length as the first wall 921 has; and a pair of third walls 923 provided integrally with the first wall 921 and the second wall 922 at right angles with respect to the lengthwise directions of the first and second walls. The first wall 921 and second wall 922 are joined with their ends abutting against each other so that they coincide in lengthwise direction with each other.
When the TV receiver 3 is packed in the cardboard box 1, the shock-absorbing packing material 92a is disposed so that the interior ridgeline formed by the interior face of the first wall 921 and the interior face of the second wall 922 abuts against a corner ridge portion of the TV receiver 3 on the front side of the upper portion thereof. In addition, the paired third walls 923 are disposed with their interior faces abutting against two opposing side faces of the TV receiver 3. Likewise, the corner ridge portion located on the rear side of the upper portion of the TV receiver 3, and left and right corner ridge portions of the lower portion of the TV receiver are held by the shock-absorbing packing materials 92b and 92c (see FIGS. 10 and 11). Because of such arrangement that the TV receiver 3 is arranged in the cardboard box 1 with shock-absorbing packing materials 92a, 92b and 92c put therebetween, physical shocks owing to drop of the cardboard box 1 and collision with other object never reach the TV receiver.
Meanwhile, a TV receiver is often out of balance in weight on the whole depending on the shapes and layout of members and constituents arranged therein, which include a CRT (Cathode Ray Tube) and a power supply device, etc. In many TV receivers, they are heavier on the front side where an image-display portion of CRT is located compared to the other sides. When a cardboard box in which a TV receiver heavier on its front side as such is packed drops from an elevation, a corner ridge portion or an apex portion of the front side of the cardboard box will come into contact with the face of the floor first.
Hence, drop tests in which actual dropping conditions of a cardboard box with a TV receiver 3 packed therein are duplicated have been carried out. FIG. 13 is an illustration for explanation of such drop tests. The indications of front and bottom faces in FIG. 13 represent the faces which the front and bottom faces of the TV receiver 3 front on.
As described above, the TV receiver 3 is out of balance in weight on the whole. Therefore, in the first test, the cardboard box is dropped so that an apex formed by its front, upper and side faces comes into contact with the face of the floor first, as shown in FIG. 13. After that, in the second test, the cardboard box is dropped so that a ridgeline formed by the front face and upper face comes into contact with the face of the floor first. In this test, the exterior face of the first wall 921 of the shock-absorbing packing material 92a abuts against the upper face of the cardboard box 1, the exterior face of the second wall 922 abuts against the front face, and the exterior faces of the paired third walls 923 abut against the two side faces.
FIG. 14 is a sectional view showing the result of the drop test. After the first test, in the shock-absorbing packing material 92a, a crack Cr arose extending from the following three ridgelines: i.e. the interior ridgeline formed by interior faces of the first wall 921 and the second wall 922; the interior ridgeline formed by interior faces of the second wall 922 and the third wall 923; and the interior ridgeline formed by interior faces of the third wall 923 and the first wall 921 located near the apex that reached the floor face first.
As shown in FIG. 14, formed was a crack Cr running from the interior ridgeline formed by the first wall 921 and the second wall 922 of the shock-absorbing packing material 92a to the exterior ridgeline formed by the first wall 921 and the second wall 922, i.e. a crack Cr running at an angle of 45 degrees with respect to the faces of the first wall 921 and the second wall 922 against which the TV receiver 3 abutted. The shock-absorbing packing material 92a with the crack Cr thus formed was used to execute the second test. Then, the cardboard box received a shock owing to the weight of the TV receiver 3 which widened the crack Cr of the shock-absorbing packing material 92a, namely a shock enough to jam the corner ridge portion of the TV receiver 3 into the crack Cr. Consequently, the crack Cr of the shock-absorbing packing material 92a reached the exterior ridgeline, and the TV receiver 3 ended up as crashing into the face of the floor and being fractured.
To avoid the transmission of a physical shock to the TV receiver 3 in the two tests, it is sufficient to make larger the thickness of the shock-absorbing packing material, thereby to enhance the shock-absorbing ability of the shock-absorbing packing material 92a. However, the increase in the thickness of the shock-absorbing packing material 92a boosts the amount of the foamed resin used to form the shock-absorbing packing material 92a and therefore raises the cost. In addition, the increase in the thickness of the shock-absorbing packing material 92a makes larger outer dimensions of the cardboard box 1. Such increase of the outer dimensions decreases the number of cardboard boxes which can be loaded in a container used for shipment of TV receivers 3, resulting in the increase in the transportation cost.
Under these circumstances, a method for reducing the fracture of the shock-absorbing packing material owing to the shock by drop has been proposed. For instance, JP-UM-A-58-65268 discloses a device in which relief portions having the shape of a groove are provided in two faces forming a ridgeline in order to disperse a stress produced in a corner portion at the time of drop, and in the other face, i.e. the remaining one of three faces forming the ridge corner of interest, a relief portion is provided diagonally with respect to the ridge corner. According to the device, the stress arising at the time of drop can be dispersed.
Also, JP-UM-A-61-77372 discloses a device in which a reentrant portion is provided in a corner portion to control the force caused by a physical shock, whereby a fracture is minimized.
Further, in the device disclosed by Japanese Utility Model Registration No. 3,072,574, a gap is formed between a corner portion of a shock-absorbing material and a corner portion of a TV receiver, thereby preventing direct transmission of the force caused by a physical shock to the TV receiver.
However, the device disclosed by JP-UM-A-58-65268 is based only on the assumption that a corner ridge portion comes into contact with a floor first, i.e. only the condition where the second test as shown in FIG. 13 is executed is assumed therein. In reality, it is conceivable that the force is applied all the three corner ridge portions as assumed in the first test. In such case, the stress can be concentrated on a corner ridge portion where no relief portion is formed.
Also, while in the device disclosed by JP-UM-A-61-77372, a reentrant portion is provided in a corner portion to control the force caused by a physical shock, the reentrant portion for controlling such force has a complicated form, and needs labor and time for manufacturing. In addition, with the device, a corner portion of a cardboard box is squashed thereby to reduce the first shock for the purpose of dispersing the force caused by a physical shock. Therefore, when drop of the cardboard box (the second test) is executed so that the corner ridge portion reaches a floor first after the first drop of the corner portion (the first test), the effect of the reentrant portion cannot be expected.
Moreover, with the device disclosed by Japanese Utility Model Registration No. 3,072,574, the transmission of the force caused by a physical shock from the shock-absorbing material to the TV receiver is delayed thereby to consume the energy when the shock-absorbing material is deformed, and thus the force caused by a physical shock is weakened. However, when the shock-absorbing material receives a physical shock such that the shock-absorbing material is fractured, the shock will be transmitted to the TV receiver.